ELM327
Pin Descriptions (continued)
If unused, pin 24 must be connected to a logic high
(VDD) level.
RS232 Rx LED (pin 25), RS232 Tx LED (pin 26),
OBD Rx LED (pin 27) and OBD Tx LED (pin 28)
These four output pins are normally high, and are
driven to low levels when the ELM327 is transmitting
or receiving data. These outputs are suitable for
directly driving most LEDs through current limiting
resistors, or interfacing to other logic circuits. If
unused, these pins may be left open-circuited.
Note that pin 28 can also be used to turn off all of the
Programmable Parameters, if you can not do so by
using the normal interface - see page 58 for details.
Unused Pins
When people only want to implement a portion of what the ELM327 is capable of, they often ask what to do with the
unused pins. The rule is that unused outputs may be left open-circuited with nothing connected to them, but unused
inputs must be terminated. The ELM327 is a CMOS integrated circuit that can not have any inputs left floating (or
you might damage the IC). Connect unused inputs as follows:
Pin
1
2
5
6
7
11
H*
12
L*
13
L*
15
H
18
H
24
H
Level
H
H*
H*
H*
H*
Note that the inputs that are shown with an asterisk (*) may be connected to either a High (VDD) or a Low (VSS)
level, but the level shown is preferred.
Ordering Information
These integrated circuits are 28 pin devices, available in either a 300 mil wide plastic (‘skinny’) DIP format or in a
300 mil (7.50 mm body) SOIC surface mount type of package. We do not offer an option for QFN packages.
To order, add the appropriate suffix to the part number:
300 mil 28 pin Plastic DIP..............................ELM327P
300 mil 28 pin SOIC....................................ELM327SM
Absolute Maximum Ratings
Storage Temperature....................... -65°C to +150°C
Note:
These values are given as a design guideline only.
The ability to operate to these levels is neither
inferred nor recommended, and stresses beyond
those listed here will likely damage the device.
Ambient Temperature with
Power Applied....................................-40°C to +85°C
Voltage on VDD with respect to VSS..... -0.3V to +7.5V
Voltage on any other pin with
respect to VSS........................... -0.3V to (VDD + 0.3V)
ELM327DSI
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
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